Microphonic switch



M. H. A. LINDSAY June 29, 1937.

MICROPHONIC SWITCH Original Filed June 22, 1934 R. J mi vd mn .Z M

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MM (bgg/WW1 ATTORNEY Patented June 29, 1937 UNITED STATES PATENT GFFICE .MICROPHONIC SWITCH Application June 22, 1934, Serial No. 731,838 Renewed February 18, 1937 5 Claims.

The present invention relates to an improvement in microphonic switches and has for its object the provision of means for accurately and easily adjusting the coacting vibration-sensitive means to desired degrees of sensitivity.

One advantage of the present structure is that, due to the manner of operative connection of the vibration-sensitive means by Contact pressure, any degree of sensitive pressure contact setting is maintained constant under all temperature variations.

Another advantage is that such pressure contact settings remain unchanged and constant under any buckling of the diaphragm from any cause.

A further advantage is that the settable pressure contact means may be adjusted to a minimum, or a maximum amount of vibration-sensitivity in adjustably utilizing the inertia of a given or fixed mass, thus excluding, or including, operative vibrations or sounds of different intensity, as desired.

These and other features of advantage will be apprehended as the description proceeds and it is obvious that modifications may be made in the structure herein, without departing from the spirit hereof or the scope of the appended claims.

In the drawing,

Fig. 1 is a sectional, plan View of the microphonic switch shown in its outer enclosing housing, taken on the line I-I, Fig. 2, looking in the direction of the arrows;

Fig. 2 is a Sectional View taken on line 2--2, Fig. 1, looking in the direction of the arrows;

Fig. 3 is a fragmentary sectional view taken on a side elevation of the inertia mechanism, and sectioned on line 3 3, Fig. 1, looking in the direction of the arrows;

Fig. 4 is a sectional view of the inertia mechanism taken on the line 4 4, Fig. 3, looking in the direction of the arrows;

Fig. 5 is an enlarged perspective view of the inertia mechanism, with one of its appurtenant jeweled bearings;

Fig. 6 is an enlarged fragmentary sectional View taken on line 6 6, Fig. l, looking in the direction of the arrows, and

Fig. '7 is a fragmentary bottom view of one corner of the screen cover plate.

As in Fig. 2, the complete detector unit comprises a preferably rectangular outer housing I, having `an integral closed top 2 and an open bottom 3, the latter being protected by an apertured cover plate 4, which aperture is protected by a meshed wire screen 5. A plurality of upright (ci. 20o-52) standards B are rigidly mounted to the corner flanges 'l of cover plate 4, the upper ends thereof being drilled and acting as stays to support one end of the coiled suspension springs 8, the other ends of said springs being attached to a dielectric, `5 supporting base ring 9, the ring being drilled at points Ill-IRL Fig. 1, thus to hold the sensitive microphone horizontally and in a resilient and shock absorbing manner.

The microphone is enclosed in a housing, hav- 10 ing a circular wall II, and an integral top I2 and has an interiorly located integral lug I3 therein, which is located against the inside face of circular wall II and the underface of top I2. The lug I3 extends radially towards the axis of 15 housing and stops short of the center thereof, as in Fig. 1. The lug has a bore I4 extending throughout its length, the purpose of which will be later described.

The resiliently supported dielectric base ring 9, Figs. 2, 3, 4 and 6 acts as a foundation ring and has afxed thereto oy means of screws, such as I6, Fig. 6, a second superimposed metallic base ring l'l, the plural screws I threadedly engaging and holding dielectric ring 9 and base ring I'I, 25 which is preferably of brass, in fixed assembly.

On each screw I6, is a small thin brass washer I8, these acting as spacers between rings 9 and I1.

Upon the top face of ring I1 is mounted a 30 metallic diaphragm I9, and upon the diaphragm is mounted a thin metallic ring gasket 20 upon which is superposed a perforated restriction disc 2l, which in turn has superposed thereon a thin metallic gasket ring 22. Upon the gasket 22 is 3- mounted a metallic restriction and support ring 23. As in Fig. 6, all of the elements above noted, from II to 23 inclusive, are held together by flat head screws 24, Figs 1 and 6, these being entered from the top of support ring 23, and being 40 threadedly connected to bottom ring I'I.

Support ring 23, as in Figs 1, 2 and 3, has mounted thereto an inertia switch mounting plate 25, which is held in spaced aperture position on said ring 23 by two screws 26-21 at oppo- 45 site ends. Under the head of screw 26 is mounted an electric connecter 28 to which is attached an electric conductor 29, for purposes later to be described The screw 26, Fig 3, is in electrical contact with 50 support ring 23, and is insulated from mounting plate 25 by two dielectric washers 30-3 and a dielectric bushing 3|, which in turn is located in a' spacer bushing 32. The other screw 2l is mounted as described above for screw 26, with 55 the exception that screw 21 does not act as a conductor Support plate 25, as in Fig 1 has its mid-portion traversed by a saw kerf or slot 34, which at its center is threaded to receive therein an adjustable inertia bar stop screw 35, Fig 4, the function of which will be described later. Pinching of the plate 25 on opposite sides of the slot, causes the screw 35 to be frictionally held in any adjusted position.

Support plate 25, Fig. 1, has affixed thereto an electric connecter 31, to which conductor 38 is connected and said conductor with conductor 29 is let out through a dielectric bushing 39 in wall I I of the housing, to a current source and a relay alarm circuit not shown.

Support plate 25, Figs. 1 and 3, supports on its underface, by means of screws iii-4I a channel shaped inertia. switch bearing member 42, the opposed, channel forming legs of which, Fig. 3, mount threaded adjustable jewel bearing set screws into the bearing seats of the jewels i5 is pivotally mounted a dual taper-ended staff 45. The staff l5 is, in turn centrally mounted transversely in the thickened central portion L38 of inertia balance bar ill, this being shown enlarged, in perspective, in Fig. 5, wherein one end of the staff Ll-Ei is shown in the jewel 45 of screw 43.

As in Figs. 4 and 5, the inertia balance bar 4l' is threaded on both of its ends .fill-55, and two inertia members in the form of balance or counter-weights Ell 5i of fixed mass, are adjustably mounted on the threaded ends 5-5. The counterweights are preferably in the form of hexagonal nuts, and, as in Fig. 5, the nuts have one side split, as at 52, whereby they may be pinched slightly to close the threaded bore a slight increment, thereby to make the members 5l hold more rmly to their threaded ends. The bearing ends supporting the adjustable jewel screws are likewise split, as in. Fig. 4 at X for the same purpose.

As in Fig. 5, one leg of the inertia balance bar has attached thereto by welding, on its underface, as shown in Fig. Li, a platinum contact point This point coacts with the platinum point 53 or the diaphragm affixed, centrally located stylus 54, to form and maintain a non-fusing, electrical contact therebetween.

Inasmuch as the mounting of the staff 45 in jewel bearings insulates the staff and inertia balance bar out of electrical contact with support ring 25, a ilexible gold wire 55 of small diameter is connected between the balance bar center 48 and the pivot bearing 42, to establish electrical contact therebetween, with a minimum of resistance to free pivotal action of the inertia balance bar 41. As described, the inertia balance bar 41, which acts as an inertia switch, is very delicately mounted for free oscillatory movement in its jewelled bearings.

The stop screw 35, Fig. 4, is adjusted to limit the upward movement of the adjacent leg of the inertia balance bar 41 which is located over the top of contact stylus 54 of the diaphragm I9.

As a means to removably aix the cover l I-I 2 to proper registered position on supporting base ring 9, a rim pin 51, Fig. 6, located in ring I1 ts a corresponding bore in the rim of wall I I, shown dotted in Fig. 1, and thereby causes the registry of the bore I4 in cover II-I2 with one of the counterbalances 5I, sol that with the both covers 2 and I I--I2 in closed position, a wrench may be inserted through joint registering bores 59 and I4, Fig. 1, to adjust said counterweight to or fro for sensitivity variation, as desired. If desired, adjusting orifices for moving both counterbalance members 5 I-5I may be provided.

A plug 60, Fig. 1, normally closes bore 54 tightly, and extends through enlarged bore Ma in housing 2, so as to be manually manipulated for removal and replacement. Thus the interior of the switch is kept dust free and tight.

To hold housing II-IZ to ring I1, two upright, hexagonal threaded end posts Si threadedly and iirmly engage the ring assembly I1 to 23 inclusive, Fig. 4, the upper ends of said posts having threaded bores, as at 62, to receive flat head screws 63 which hold the cover II-i2 to ring I1.

The screen cover 4 is held to the open bottom of housing 2 by four screws 64, shown dotted in Fig. 1, at each corner. The screen 5 is aliX-ed to the frame or" cover plate 4 by escutcheon pins a, as in Figs. 2 and '7.

As herein shown and described the microphonic switch is intended to guard desired protected areas such as bank vaults, safes and other closed places, and is normally connected up in primary closed circuit, not shown, to be broken when vibrations occur to operate the diaphragm, which moves the inertia switch about its axis, disconnecting the contact oi tip 53 and Contact 49, this breaking of the circuit being effective to operate a secondary electric, relay alarm circuit,

not shown, and thus cause visible and audible alarms to be set oi.

The current ilows from a source not shown, through conductor 29, through screw through bottom ring assembly phragm il), through stylus 54, through the inertia switch element i1 through wire 55 to bearing 42, to support bar .25 and from thence through. connecter 31 and conductor 38, back to source of current.

Due to the settability ci the counter weights. upon assembly and the later adjustability ior desired degree of vibration sensitivity, the herein described microphonic switch may be set to meet any condition ci requirements.

As shown above, the housing i is closed at one sido by the thin metal diaphragm i9. Immediately behind the diaphragm i9 and separated from it by a thin air gap is the perforated plate 2l which serves the double function of protecting the diaphragm from injury if struck from the outside, since its motion would then be limited by the distance to this plate, and also to provide a suitable damping for the diaphragm to suppress its amplitude at its resonant frequency. Were this damping not provided, the detector might be super-sensitive at the resonant frequency, and thereby initiate false alarms, if even weak sounds of this frequency continued for some time. Immediately above this plate 2| and separated from it by a small distance, is the restriction or baille ring 22, which permits the air which is compressed between the diaphragm and the plate to vent into the housing cavity containing the detector mechanism 51 to 53. The size of this housing cavity has been determined by acoustical measurements so as to provide the necessary amplification of low frequency sounds to insure a relatively uniform frequency characteristic.

Having thus described the invention what is claimed is:

1. A microphonic switch detector comprising a diaphragm actuatable by sound vibrations; a contact part operatively connected to the diai1 to 23, including diaphragm; a movable inertia switch member; a contact device connected to said member and in contact with the Contact part, whereby the in,- ertia member may be moved by the diaphragm to vary the pressure between said device and said Contact part; and means for adjusting the pressure of said device on the Contact part and adjusting the inertia effect of said member independently of said pressure.

2. A microphonic switch detector comprising a diaphragm actuatable by sound vibrations; a contact part operatively connected thereto; an intermediately fulcrumed inertia switch member; a contact device operatively connected with the member in Contact with the contact part of the diaphragm whereby the member may be moved by the diaphragm to vary the pressure between said device and said Contact part; and weights adjustable on opposite arms respectively of the member and disposed in position for adjusting the pressure of said member on the contact part of the diagram and adjusting the inertia effect on said member independently of said pressure.

3. A microphonic switch detector comprising a supporting ring; a metal diaphragm supported across said ring; a perforated plate immediately behind said diaphragm and forming with the diaphragm a thin air gap, and a contact switch operatively connected to the diaphragm.

4. A microphonic switch detector comprising a housing closed except at one side; a metal diaphragm closing said side; a perforated plate immediately behind said diaphragm said plate forming, with said housing, an amplifying cavity.

5. A microphonic switch detector comprising a diaphragm actuatable by sound vibrations and having a contact part thereon; a movable inertia switch member in contact with the contact part, whereby the inertia member may be moved by the diaphragm to dise-ngage said member from the contact part; and means for adjusting the pressure of said member on the Contact part; a movable weight; and adjustable means for adjustably connecting the weight to the switch member for adjusting the inertia effect of said member independently of said pressure.

MAXWELL H. A. LINDSAY. 

